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i.his.rgb is an image processing program that
processes three input raster map layers as hue, intensity
and saturation components and produces three output raster
map layers representing the red, green and blue components
of this data. The output raster map layers are created by
a standard hue-intensity-saturation (HIS) to red-green-blue
(RGB) color transformation. Each output raster map layer
is given a linear gray scale color table. The current
geographic region and mask settings are respected.

It is not possible to process three bands with
i.his.rgb and then exactly recover the original
bands with i.rgb.his.
This is due to loss of precision because of integer
computations and rounding. Tests have shown that more than
70% of the original cell values will be reproduced exactly
after transformation in both directions and that 99% will
be within plus or minus 1. A few cell values may differ
significantly from their original values.